The invention relates to a coating composition, and especially to a coating composition useful in ink jet applications. Specifically the coating composition contains pigment and a water-dispersible hydrophobically modified copolymer prepared from at least one vinyl monomer, at least one carboxylic acid monomer, and 1 to 15 percent of one or more monomers containing a sterically hindered amine functionality. The coating is especially useful for ink-jet printing on paper, paperboard, textiles, non-wovens, glass, films, laminates, and wood.
Fibrous substrates, such as paper, are coated to produce a smoother and less absorbent surface on which to apply printing inks and other functional coatings. The coating composition typically comprises naturally occurring or man-made pigments, synthetic or natural polymer coating binders, water, and small amounts of miscellaneous additives. The pigments are used to fill and smooth the uneven surface of the fibrous paper web, while the binder is used to hold the pigment particles together and to hold the coating layer to the paper. Typical paper coating binders are composed of synthetic polymers, natural polymers, or a mixture of these components.
The paper coating must also act to fix the ink on the surface, preventing it from running on the surface or bleeding though a substrate. This fixing produces good print definition and print quality. Since the inks used in most printing applications are anionic, one means of fixing the inks to the substrate is to have a coating with some cationic character. There are several examples of cationic paper coatings in the art. U.S. Pat. No. 6,153,288 discloses ink-receptive compositions having a pigment dispersed in a binder containing a vinyl acetate emulsion binder, and a water soluble cationic copolymer. Coating compositions containing polymers having low levels of tertiary amine functionality, up to 0.4 mole percent, are disclosed in U.S. Pat. No. 4,944,988. U.S. Pat. No. 5,660,928 discloses a multi-layer paper coating for ink jet printing which contains as a third layer a cationic water soluble polymer, U.S. patent application Ser. No. 10/152,354, discloses cation ic coating compositions containing polymers formed from vinyl ester monomers and from 0.4 to 3 mole percent of a cationic monomer, which preferably contains primary, secondary, or tertiary amine groups.
Amphoteric water soluble polymers useful for ink absorbing layers, and formed from anionic and cationic monomers with an aziridine crosslinking agent are disclosed in JP 07184082. JP 11222346 discloses a cold sealing adhesive for color ink-jet containing an amphoteric polymer prepared from anionic monomer and dimethylaminoethylbenzyl chloride. U.S. Pat. No. 4,305,860 describes the use of polyampholytes as paper-making aids. These polymers are made from an anionic monomer, a cationic monomer, a hydrophobic monomer, and a hydrophilic monomer. A problem with amphoteric, betaine, and ampholytic polymers is that they contain cationically charged species, which can react with anionic pigments, binder, cobinder, and other components of the coating composition.
There is a need for an aqueous-based, water-insoluble non-ionic polymer useful for ink-receptive coatings, which provides excellent print quality.
Surprisingly it has been found that copolymers containing a sterically hindered amine functionality and a carboxylic acid functionality, remain non-ionic in a coating composition having a neutral or alkaline pH. These copolymers then become cationic when in the presence of acidic inks. Coatings containing these polymers provide excellent ink-retention without the negative effects found with cationically charged polymers. These coatings may be used on fibrous substances, as well as films and laminates.
The present invention is directed to an ink-receptive coating composition useful on a variety of substrates. The coating composition contains 25 to 75 percent by weight of pigment, and 0.5 to 25 weight percent of a copolymer formed from 1 to 15 percent by weight of one or more monomers having sterically hindered secondary amine groups, and 10 to 40 percent by weight of one or more carboxylic acid monomers.
The invention is also directed to a substrate having coated directly thereon a coating composition containing 25 to 75 percent by weight of pigment, and 0.5 to 25 weight percent of a polymer comprising 1 to 15 percent by weight of one or more monomers having sterically hindered secondary amine groups, and 10 to 40 percent by weight of one or more carboxylic acid monomers.